RE: Deception units
This means that up to 5 hex's from that deception unit your opponents units may suffer the deception effects as explained in the manual.
It depends on what part of the deception effects you wish to apply to the current game, if for example you wish to interfere with an engineer damaging a bridge then you need that unit to be within 5 hex's of that bridge, if you want to disrupt units in T mode then you need to be 5 hex's within the range of a road that you suspect your opponent might use?
As far as I know the deception effects are not range dependent so if possible you want to keep your unit out of LOS so your opponent does not know that the deception effects are active in hex's he is going to access.
I should say I am only experienced with the deception effects in relation to partisan units, reading the manual again I see that the deception range is also used to determine where a deception units can be deployed which is different to partisans units that are deployed to the map and move as "normal" units do.
When your opponents units in T mode are disrupted by the deception feature they will be informed of this fact, however I have no idea if the same applies to an engineer unit trying to damage a bridge?
As deception units/partisans only appear in a few titles there has not been much chat about the deception feature over the years.